Corps of soldiers love my job getting harder, permanently (13)

I believe the answer is:

thermosetting

'getting harder permanently' is the definition.
(process of irreversible hardening)

'corps of soldiers love my job' is the wordplay.
'corps of soldiers' becomes 'therm' (the Royal Marines).
'love' becomes 'o' (In tennis, 'love' means 'zero').
'my job' becomes 'setting' (the crossword setter's job).
'therm'+'o'+'setting'='THERMOSETTING'

I've seen this clue in The Times.

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